A recent study published in The Astrophysical Journal investigates whether water-rich exoplanets can survive in orbits around white dwarf stars, which are the remnants of stars similar to our Sun. The research team aimed to determine if small, rocky planets in close proximity to these stars might support life.
The study highlights the conditions under which first-generation exoplanets—those that formed alongside their host stars—can retain water while migrating inward towards a white dwarf. To achieve this, the researchers utilized mathematical models to analyze how these planets could maintain their water content during the transition from a Sun-like state to that of a white dwarf.
First-generation planets are significant as they have survived the complete lifecycle of their host stars, including the transformation into red giants before becoming white dwarfs. The researchers calculated the effective temperature of these planets, which is crucial for estimating their habitable zones. Notably, the habitable zone can shift as the star evolves from a Sun-like star to a white dwarf.
Additionally, the team modeled the evaporation of water from the surface of these planets due to changing solar radiation levels. They also examined how close encounters between planets—known as scattering events—could impact the retention of water on these worlds.
The findings indicate that planets the size of Earth or Mars would require significantly larger quantities of water than Earth possesses or must start their orbits much farther from the white dwarf. The study revealed that the intense radiation from a white dwarf would likely evaporate all water from these planets.
White dwarfs are the dense remnants of Sun-like stars that have exhausted their nuclear fuel and shed their outer layers. These stars are roughly the size of Earth but contain about 60 percent of the mass of their progenitor stars, leading to extreme densities—one teaspoon of white dwarf material can weigh several tons.
While our Sun is around 4.6 billion years old, scientists project it will not transition to the white dwarf phase for another 5 to 7 billion years. This research contributes to the ongoing efforts of astronomers to identify potential habitable worlds and the possibility of life beyond Earth. Although previous searches have focused on Sun-like stars for Earth-like planets, this study suggests that white dwarfs could also be viable candidates for astrobiological studies. Future research may further explore the potential for water retention on Earth-like planets orbiting these stars.
As researchers continue to seek insights into exoplanets that may harbor life, the quest to understand the habitability of planets around white dwarfs remains an exciting frontier in astronomy.
